In power semiconductor devices used for controlling electrical power, continuing efforts have been made to reduce on-resistance in order to reduce power losses during switching operations. For example, by using a trench gate as a gate structure, channel density can be increased in comparison to a gate with a planar structure. Furthermore, by further miniaturizing element structures, it is possible to greatly reduce the on-resistance.
On the other hand, in power semiconductor devices with low breakdown voltages, such as the power MOSFET, the need for fast operation for applications in switching power supplies and DC-DC converters continues to grow. In this case, elements that are not destroyed by surge voltages with narrow pulse widths that occur during high-speed switching are desired.
To respond to these needs, there is a need for a semiconductor device with a high withstand capability for avalanche breakdown. Thus, it is desirable to increase the breakdown voltage at the termination portions, and especially at corner portions, where the electric field distribution is asymmetric and electric field concentrations easily occur.